The Oak Processionary Moth is a nasty little beast. It's native to Europe, but didn't show up in the United Kingdom until 2006, when a few eggs hitched a ride on oak trees transplanted to London. Since then, it's been causing environmental chaos. Now it's threatening to seriously screw up the Summer Olympics.

Recent reports have brought up the concern that its larvae—toxic caterpillars that can cause serious illness—are going to invade the London Olympics and make audience members swell up and itch to an extent where they can't enjoy the games, to say nothing of the athletes. If they're right, it'll be a serious problem. But how much damage can a little caterpillar do? Quite a bit, actually.

Bad hair

It's not like these caterpillars will be crawling around feasting on human flesh. It's actually more insidious. The insects' hairs—tiny sharp barbs that contain a toxin called thaumetopoein—can really ruin your day: If you come into contact with them you could come down with itchy skin lesions, a sore throat, breathing difficulty, and severe nausea. Each Oak Processionary larvae is covered with approximately 62,000 strands of toxic fuzz, which the caterpillar can eject. The hairs stay chemically toxic for five years after falling to the ground. Even worse? Once they detach, they're blown on the wind, so even if you're nowhere close to touching a colony, you could still get sick.

And this caterpillar isn't just harmful to humans: it's also a major threat to trees. Foresters are terrified by the larvae's ability to completely defoliate oak trees. This ugly caterpillar can eat. Oak trees without leaves don't live long, and the Oak Processionary caterpillar did serious damage to British forests in the first three years of its invasion.

What England is doing to prepare

The story of the Oak Processionary Moth in many ways resembles North America's difficulties with the Gypsy Moth. Both are alien species that are completely wrecking forests that they're not native to. And both seem almost unbeatable.

Despite a concerted effort by UK officials to spray the caterpillars shortly after they hatch, the pestilence is spreading. Authorities have tried using pheromone traps to nab the bastards, but the United Kingdom Forestry Commission admits that it has been ineffective:

"Over the past five years it has become clear that the network of pheromone traps has not captured as many moths as expected, nor has it proved particularly effective at monitoring their spread."

The infestation is so bad that the commission has had to revise its long-standing policy regarding the transportation of flora. As of 2008, no trees can enter the United Kingdom without a special "tree passport," a document that describes the provenance of a plant and certifies that it is free of pests and passengers.

Where do they hang out?

Being named the Oak Processionary moth, you'd expect that these caterpillars like oak trees. They do, but they've also been spotted on birches, hazel trees and chestnut trees. A recent alert by the UK Forestry Commision warns of colonies in west and south London, and Pangbourne in Berkshire. You can spot infected trees between April and August (the caterpillar's life span) by the disgusting white webs around their branches.

In other words, they're pretty much everywhere. Including where spectators and competitors will be gathering in droves in just a few months.

What should I do if I see them?

First, relax. There have been no confirmed deaths due to the Oak Processionary moth. Second, get as far away as you can—its hairs can travel on the wind and make your throat swell up. While you're at it, make sure your dog or cat stays away too; your furry friends are not immune to its toxin. Third, there's a large-scale effort to eliminate this pest, so you should report it to authorities immediately. They'll remove the colony for you, and you'll be helping out by reporting it.